refactor(sync): rename ConnectedDegraded to ConnectedHistoricSyncFailures

Resolves naming conflict with RelayHealthState::Degraded by using a more
explicit name that clearly indicates the connection status relates to
historic sync failures, not connection health degradation.

Changes:
- ConnectionStatus::ConnectedDegraded → ConnectedHistoricSyncFailures
- Updated all documentation and comments
- Updated Prometheus metric descriptions
- Metric value remains 4 for backward compatibility

This makes it clear that:
- ConnectedHistoricSyncFailures = connection lifecycle (missing historic data)
- RelayHealthState::Degraded = connection health (reliability issues)

These are orthogonal concerns - a relay can be ConnectedHistoricSyncFailures
but Healthy, or Connected but Degraded.

2 files changed, 9 insertions, 9 deletions

diff --git a/src/sync/metrics.rs b/src/sync/metrics.rs
index 0f56911..7907d8e 100644
--- a/src/sync/metrics.rs
+++ b/src/sync/metrics.rs
@@ -53,7 +53,7 @@ impl SyncMetrics {
         let relay_connected = IntGaugeVec::new(
             Opts::new(
                 "ngit_sync_relay_connected",
-                "Relay connection status (0=disconnected, 1=connecting, 2=syncing, 3=connected, 4=connected_degraded)",
+                "Relay connection status (0=disconnected, 1=connecting, 2=syncing, 3=connected, 4=connected_historic_sync_failures)",
             ),
             &["relay"],
         )?;
@@ -208,7 +208,7 @@ impl SyncMetrics {
     /// - Connecting = 1 (connection attempt in progress)
     /// - Syncing = 2 (connected, historic sync in progress)
     /// - Connected = 3 (connected, historic sync complete)
-    /// - ConnectedDegraded = 4 (connected, historic sync failed but live sync active)
+    /// - ConnectedHistoricSyncFailures = 4 (connected, historic sync had failures but live sync active)
     ///
     /// This is separate from health state and provides more granular connection lifecycle tracking.
     ///
@@ -223,7 +223,7 @@ impl SyncMetrics {
             ConnectionStatus::Connecting => 1,
             ConnectionStatus::Syncing => 2,
             ConnectionStatus::Connected => 3,
-            ConnectionStatus::ConnectedDegraded => 4,
+            ConnectionStatus::ConnectedHistoricSyncFailures => 4,
         };
         self.relay_connected
             .with_label_values(&[relay])
diff --git a/src/sync/mod.rs b/src/sync/mod.rs
index 2031ef4..0e5b9bb 100644
--- a/src/sync/mod.rs
+++ b/src/sync/mod.rs
@@ -94,8 +94,8 @@ pub enum ConnectionStatus {
     Syncing,
     /// Successfully connected, historic sync completed
     Connected,
-    /// Successfully connected, historic sync failed but live sync active
-    ConnectedDegraded,
+    /// Successfully connected, historic sync had failures but live sync active
+    ConnectedHistoricSyncFailures,
 }
 
 impl ConnectionStatus {
@@ -103,7 +103,7 @@ impl ConnectionStatus {
     pub fn is_live_sync_active(&self) -> bool {
         matches!(
             self,
-            ConnectionStatus::Syncing | ConnectionStatus::Connected | ConnectionStatus::ConnectedDegraded
+            ConnectionStatus::Syncing | ConnectionStatus::Connected | ConnectionStatus::ConnectedHistoricSyncFailures
         )
     }
 }
@@ -877,7 +877,7 @@ impl SyncManager {
                 tracing::warn!(
                     relay = %relay_url,
                     batch_id = batch_id,
-                    "Batch failed - will transition to ConnectedDegraded instead of Connected"
+                    "Batch failed - will transition to ConnectedHistoricSyncFailures instead of Connected"
                 );
             }
 
@@ -963,7 +963,7 @@ impl SyncManager {
             if state.connection_status == ConnectionStatus::Syncing {
                 // Check if any batches failed during historic sync
                 let new_status = if state.historic_sync_had_failures {
-                    ConnectionStatus::ConnectedDegraded
+                    ConnectionStatus::ConnectedHistoricSyncFailures
                 } else {
                     ConnectionStatus::Connected
                 };
@@ -979,7 +979,7 @@ impl SyncManager {
                     had_failures = state.historic_sync_had_failures,
                     status = ?new_status,
                     "Historic sync complete - transitioned to {} status",
-                    if state.historic_sync_had_failures { "ConnectedDegraded" } else { "Connected" }
+                    if state.historic_sync_had_failures { "ConnectedHistoricSyncFailures" } else { "Connected" }
                 );
                 
                 // Update metrics